Ion exchange polymer dispersion, process for its production and its use

Abstract

A thickened ion exchange polymer dispersion is obtained by applying ultrasonic vibration or a shearing force to an ion exchange polymer dispersion having a fluorinated polymer having sulfonic acid groups as an ion exchange polymer uniformly dispersed in a dispersion medium so that the viscosity of the dispersion at 25° C. at a shear rate of 10 (1 / s) increases 2-2000 times in a thickening step. When formed into a membrane, the dispersion can forms an ion exchange membrane having a uniform and small thickness, high strength, which is free from cracking and shows constant swelling in water and steam. Further, a layer formed by applying a coating solution containing this dispersion and a catalyst powder comprising catalyst metal particles and a carbon support loaded with the catalyst metal particles to a substrate can be used to prepare a membrane-electrode assembly as a catalyst layer for at least one of the cathode and the anode by providing the catalyst layer adjacently to an ion exchange membrane. Because the catalyst layer is highly strong, has few defects and is excellently smooth, a high-performance membrane-electrode assembly for solid polymer electrolyte fuel cells can be obtained.

Description

TECHNICAL FIELD[0001]The present invention relates to an ion exchange polymer dispersion, a process for its production, a process for producing an ion exchange membrane made of the ion exchange polymer and a process for producing a membrane-electrode assembly for solid polymer electrolyte fuel cells prepared by using the ion exchange polymer.BACKGROUND ART[0002]The hydrogen-oxygen fuel cell receives attention as a power generating system having little adverse effect on the global environment because in principle, its reaction product is water only. Solid polymer electrolyte fuel cells were once mounted on spaceships in the Gemini project and the Biosatellite project, but their power densities at the time were low. Later, more efficient alkaline fuel cells were developed and have dominated the fuel cell applications in space including space shuttles in current use.[0003]Meanwhile, with the recent technological progress, solid polymer fuel cells are drawing attention again for the fol...

AI Technical Summary

Benefits of technology

The present invention provides an ion exchange polymer dispersion for the formation of an ion exchange membrane with uniform and small thickness, high strength, and constant swelling in water or steam. The process for producing the dispersion involves thickening an initial dispersion of an ion exchange polymer and a fluorinated polymer having sulfonic acid groups in a dispersion medium by applying ultrasonic vibration or a shearing force to increase the viscosity of the dispersion. The resulting membrane has smooth layers and is resistant to cracking. The invention also provides a membrane-electrode assembly for solid polymer electrolyte fuel cells with smooth and uniform electrodes containing an ion exchange polymer.

Problems solved by technology

Solid polymer electrolyte fuel cells were once mounted on spaceships in the Gemini project and the Biosatellite project, but their power densities at the time were low.

However, the method (1) has a minimum limit on the thickness of obtainable membranes because thin membranes are difficult to handle during hydrolysis and acid treatment.

Further, because the hydrolysis and the acid treatment cannot be carried out successively at a high rate, the method is disadvantageous in terms of cost.

However, thin membranes obtained by this method have defects such as low strength, vulnerability to cracking, and change in swelling in water or steam with time, presumably, though not precisely, because the dispersion of the polymer having sulfonic acid groups has a structure having micelles of the polymer dispersed in the dispersion (JP-B-61-40267).

However, in these methods, because a solvent having a relatively high boiling point is added, a residue of the solvent remains in a membrane cast at a low temperature, or casting requires a long time or a high temperature not to leave a residue of the solvent.

Accordingly, there is a problem with production efficiency.

However, there was a problem that burning of a residual solvent which can occur at an elevated temperature in the presence of the catalyst deteriorates the performance.